US20020132113A1 - Method and system for making a micromachine device with a gas permeable enclosure - Google Patents

Abstract

A method for coating a micro-electromechanical system (MEMS) device is provided. A coating material, such as a ceramic slurry, may be utilized to form a gas permeable enclosure or shell around the device after the coating material hardens. A vacuum may be applied near the device to exert an attractive force on the coating material to aid in homogenously distributing the coating material over the device. In addition, a vibration may be applied to the device to aid in distributing the coating material. If the device is attached to a substrate, a hole may be formed through the substrate with one opening near the device and a second opening located elsewhere. The vacuum may then be applied to the second opening to draw the coating material over the device and towards the first opening.

Description

CROSS-REFERENCE
• This application is a continuation-in-part of U.S. patent application Ser. No. 09/688,722, filed on Oct. 16, 2000, which is a continuation-in-part of U.S. application Ser. No. 09/483,640, filed Jan. 14, 2000, and issued on Mar. 6, 2001, as U.S. Pat. No.[0001]6,197,610.
BACKGROUND
• The present disclosure relates generally to semiconductor processing, and more particularly, to a system and method for making micro-electromechanical system (MEMS) devices with gas-permeable enclosures.[0002]
• Integrated circuit devices may need one or more small gaps placed within the circuit. For example, MEMS devices and other small electrical/mechanical devices may incorporate a gap in the device to allow the device to respond to mechanical stimuli. One common MEMS device is a sensor, such as an accelerometer, for detecting external force, acceleration or the like by electrostatically or magnetically floating a portion of the device. The floating portion can then move responsive to the acceleration and the device can detect the movement accordingly. In some cases, the device has a micro spherical body referred to as a core, and a surrounding portion referred to as a shell. Electrodes in the shell serve not only to levitate the core by generating an electric or magnetic field, but to detect movement of the core within the shell by measuring changes in capacitance and/or direct contact of the core to the shell. A coating may be applied to the MEMS device to provide a protective and insulating enclosure around the device and its components.[0003]
• Due in part to the size of MEMS devices, imperfections created by the manufacturing process may create problems in the structure of a MEMS device that might be insignificant in larger scale applications but may render the MEMS device unusable. Such problems may, for example, include flaws in a coating layer of a MEMS device.[0004]
• Accordingly, certain improvements are desired for MEMS devices and their manufacturing. For one, it is desirable to provide a coating that is relatively homogeneous and free of voids. Furthermore, it is desired to provide protection, to provide a coating of a desired thickness, to provide high productivity, and to provide a manufacturing process that is more flexible and reliable.[0005]
SUMMARY
• A technical advance is provided by a method for coating a micro-electromechanical system device. In one embodiment, the method comprises providing the device mounted on a substrate, where the substrate includes an aperture having a first opening proximate to the device and a second opening. A vacuum is applied to the second opening and a coating material is applied to the device. The vacuum aids in the homogeneous distribution of the coating material on the device by drawing a portion of the coating material over the device towards the first opening.[0006]
• In another embodiment, the method includes applying a vibration to the device to aid in the distribution of the coating material over the device.[0007]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a flowchart of a manufacturing process for implementing one embodiment of the present invention.[0008]
• FIGS.[0009]2-5,6a,6b,7a, and7bare cross sectional views of a spherical shaped accelerometer being manufactured by the process of FIG. 1.
• FIG. 8 is a flowchart of a manufacturing process for implementing one embodiment of the present invention of FIG. 1.[0010]
• FIG. 9 is a cross sectional view of a spherical shaped accelerometer being manufactured by the processes of FIGS. 1 and 8.[0011]
• FIG. 10 is a flowchart of a method for applying an enclosure around a micro-electromechanical device.[0012]
• FIG. 11 is a cross sectional view of a spherical shaped accelerometer without the enclosure provided by the method of FIG. 10.[0013]
• FIG. 12 is a cross sectional view of the accelerometer of FIG. 11 with the enclosure.[0014]
• FIG. 13 is a cross-sectional view of a spherical shaped accelerometer with multiple gas-permeable enclosures.[0015]
• FIG. 14 is a cross-sectional view of a spherical shaped accelerometer with a hermetic seal.[0016]
DETAILED DESCRIPTION
• The present disclosure relates to semiconductor processing, and more particularly, to a system and method for making a micro-electromechanical system (MEMS) devices with gas-permeable enclosures. It is understood, however, that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.[0017]
• Referring to FIG. 1, the[0018]reference numeral10 refers, in general, to a manufacturing process for making MEMS devices such as is described in U.S. Pat. No. 6,197,610, issued on Mar. 6, 2001, and also assigned to Ball Semiconductor, Inc., entitled “METHOD OF MAKING SMALL GAPS FOR SMALL ELECTRICAL/MECHANICAL DEVICES” and hereby incorporated by reference as if reproduced in its entirety. For the sake of example, FIGS.2-7bwill illustrate a spherical shaped accelerometer that is being made by themanufacturing process10. It is understood, however, that other MEMS devices can benefit from the process. For example, clinometers, ink-jet printer cartridges, and gyroscopes may be realized by utilizing a similar design.
• At[0019]step12 of themanufacturing process10, a substrate is created. The substrate may be flat, spherical or any other shape. Referring also to FIG. 2, for the sake of example, a spherical substrate (hereinafter “sphere”)14 will be discussed. Thesphere14 is one that may be produced according to presently incorporated U.S. Pat. No. 5,955,776, issued on Sep. 21, 1999, and also assigned to Ball Semiconductor, Inc., entitled “SPHERICAL SHAPED SEMICONDUCTOR INTEGRATED CIRCUIT,” and to continue with the present example, is made of silicon crystal. On anouter surface16 of thesphere14 is a silicon dioxide (SiO2) layer. It is understood that the presence of theSiO2 layer16 is a design choice and may not be used in certain embodiments. For example, theSiO2 layer16 may not be used if thesubstrate16 will not react with an etchant.
• At[0020]step18 of FIG. 1, a first group of processing operations are performed on the substrate. This first group of processing operations represents any operations that may occur before a sacrificial layer is applied (described below, with respect to step22). Referring also to FIG. 3, in continuance with the example, a first metal layer20 (hereinafter “metal 1”) is deposited on top of theSiO2 layer16. Themetal 1layer20 may be a material such as a chromium film, although other materials may be used. This metal deposition may be created by sputtering. Several different methods, such as is described in U.S. Pat. No.6,053,123, issued on Apr. 25, 2000, and also assigned to Ball Semiconductor, Inc., entitled “PLASMA-ASSISTED METALLIC FILM DEPOSITION” and hereby incorporated by reference as if reproduced in its entirety.
• At[0021]step22 of FIG. 1, a sacrificial layer is applied to the substrate. The sacrificial layer may be applied on top of the previous layers (if any). In continuance with the example of FIG. 3, asacrificial polysilicon layer24 is applied on top of themetal 1layer20. Thesacrificial layer24 may be applied by sputtering or any conventional manner, such as is described in the presently incorporated patents. Polysilicon is chosen because it reacts well with an etchant discussed below with respect to step50, but it is understood that other materials can also be used.
• At[0022]step26 of FIG. 1, a second group of processing operations is performed on the substrate. This second group of processing operations represents any operations that may occur after the sacrificial layer is applied. In continuance with the example of FIG. 3, a second metal layer28 (hereinafter “metal 2”) is deposited on top of thesacrificial layer24. Themetal 2layer28 may be a gold-chromium (Au/Cr) material, although other materials may be used and themetal 2 layer may have a different composition than themetal 1layer20.
• At[0023]step30 of FIG. 1, one or more layers of material applied in the second group of processing operations are patterned. The patterning occurs before the removal of the sacrificial layer (described below, with respect to step50). Referring also to FIG. 4, themetal 2layer28 is patterned to produce a plurality ofelectrodes28a,28b,28c,28d, and28e.
• The[0024]metal 2layer28 can be patterned by several different methods. For example, a resist coating may be applied to themetal 2layer28, such as is shown in U.S. Pat. No. 6,179,922, issued on Jan. 30, 2001, entitled “CVD PHOTO RESIST DEPOSITION” and/or U.S. Pat. Ser. No. 09/584,913, filed on May 31, 2000, entitled “JET COATING SYSTEM FOR SEMICONDUCTOR PROCESSING,” which are both assigned to Ball Semiconductor, Inc., and hereby incorporated by reference as if reproduced in their entirety.
• Once the resist coating has been applied, the coating may be exposed using a conventional photolithography process. In the present embodiment, the etching should not remove the[0025]sacrificial layer24. For example, photolithography processes, such as shown in U.S. Pat. No. 6,061,118, issued on May 9, 2000, entitled “REFLECTION SYSTEM FOR IMAGING ON A NONPLANAR SUBSTRATE” and/or U.S. Pat. No. 6,251,550, issued on Jun. 26, 2001, entitled “MASKLESS PHOTOLITHOGRAPHY SYSTEM THAT DIGITALLY SHIFTS MASK DATA RESPONSIVE TO ALIGNMENT DATA,” which are both assigned to Ball Semiconductor, Inc., and hereby incorporated by reference as if reproduced in their entirety, may be used. In the present example, themetal 2layer28 is the only layer that is patterned. For this reason, there is no need for alignment. It is understood, however, that different embodiments may indeed require alignment. For example, if thesphere14 is flat, or if themetal1layer20 is also patterned, themetal 2layer28 may indeed need to be patterned. Also, if the entire resist coating cannot be exposed at the same time, alignment between exposures may be required.
• Once the resist coating has been fully exposed (to the extent required), the exposed surface can be developed and etched according to conventional techniques. For example, the exposed photo resist and Au/[0026]Cr metal 2 layer may be etched according to a technique such as shown in U.S. Pat. No. 6,077,388, issued on Jun. 20, 2000, and also assigned to Ball Semiconductor, Inc., entitled “SYSTEM AND METHOD FOR PLASMA ETCH ON A SPHERICAL SHAPED DEVICE” and hereby incorporated by reference as if reproduced in its entirety. Once etching is complete (and cleaning, if required), theelectrodes28a,28b,28c,28d, and28emay be fully processed.
• At[0027]step34 of FIG. 1, the substrate and processed layers are assembled, as required by a particular application. Referring also to FIG. 5, a plurality ofbumps36a,36bare applied to theelectrodes28a,28b, respectively. In the present example, the bumps are gold, but it is understood that other materials may be used, such as solder. Thebumps36a,36bmay also be applied toelectrodes38a,38b, respectively, of asecond substrate40. Because thesacrificial layer24 still exists, the process of applying thebumps36a,36bto theelectrodes28a,28band38a,38bis relatively straight forward. For the sake of example, the bump application may be performed by the method described in U.S. Pat. No. 6,251,765, issued on Jun. 26, 2001, and also assigned to Ball Semiconductor, Inc., entitled “MANUFACTURING METAL DIP SOLDER BUMPS FOR SEMICONDUCTOR DEVICES” and hereby incorporated by reference as if reproduced in its entirety.
• Once the bumps have been applied and attached, a[0028]protective coating42 may be applied as will be described in greater detail in reference to FIGS.8-11. In the present example of FIG. 5, theprotective coating42 covers all of theelectrodes28a,28b,28c,28d,28e(and thus the underlying layers and substrates), thebumps36a,36b, and at least a portion of theelectrodes38a,38b. In the present example, theprotective coating42 is ceramic, but may be epoxy resin, polyimide, or any other material. Theprotective coating42 may be applied in any manner, including dipping or spraying the coating onto the components to be coated.
• The above-described[0029]manufacturing process10 uses conventional processing operations in a new and modified sequence. It is recognized that the processing operations referenced above, or different operations that better suit particular needs and requirements, may be used.
• At[0030]step44 of FIG. 1, holes are created in one or more of the processed layers. Referring also to FIGS. 6aand6b, holes46 are made through theprotective coating42 and extending between theelectrodes28a,28b,28c,28d,28eto thesacrificial layer24. In the preferred embodiment, these holes are made using alaser48. Thelaser48 is positioned to burn the hole directly through theprotective coating42 to reach thesacrificial layer24. Other ablation methods include particle injection or other chemical and/or mechanical techniques.
• At[0031]step50 of FIG. 1, the sacrificial layer is removed. Referring also to FIGS. 7aand7b, thesacrificial layer24 is etched through theholes46. In continuance of the above examples where thesacrificial layer24 is polysilicon, a xenon difluoride (XeF2)dry etchant52 can be used. The XeF2dry etchant52 has extremely high selectivity. It readily reacts with crystalline silicon and polysilicon, but does not react with themetal2layer28, theprotective coating42, or various other materials. It is understood that other etchants may be used.
• As a result, the[0032]sacrificial layer24 is removed and agap54 is formed in its place. Thegap54 separates thesphere14,SiO2 layer16, andmetal 1 layer20 (collectively the “core”) from themetal 2 layer28 (the “shell”). In the present embodiment, thegap54 extends around the entire core to complete the construction of a three-axis accelerometer56.
• Referring now to FIGS. 8 and 9, in another embodiment, the[0033]reference numeral60 refers, in general, to one embodiment of a manufacturing process for producing a gas permeable shell that surrounds MEMS devices. Atstep62, a first solid is dissolved in a solvent to form a solution. The first solid may be boron oxide (B203) or any other material. The solvent may be iso-propyl (IPA) alcohol or any other solvent.
• At[0034]step64, the solution fromstep62 is mixed with a second solid to form a slurry. The second solid may be alumina cement or any other material. By controlling the amount of mixing instep64, the size of the pores of the gaspermeable shell42 can be controlled. The size of the pores of the gaspermeable shell42 can be also be controlled by the composition of the slurry.
• At[0035]step66, the slurry fromstep48 is poured onto the substrate and processed layers. The slurry covers all of theelectrodes28a,28b,28c,28d,28e, and28f(and thus the underlying layers and substrates), thebumps36a,36b, and at least a portion of theelectrodes38a,38b. Atstep68, the slurry covered substrate and processed layers are dried at room temperature. The second solid may be dispersed in the gaspermeable shell42.
• At[0036]step70, the substrate and processed layers are exposed to the solvent. The solvent re-dissolves the first solid leaving behind the gaspermeable shell42. The gaspermeable shell42 has pores that are now interconnected and extend between theelectrodes28a,28b,28c,28d,28eand28fto thesacrificial layer24.
• In yet another embodiment, alumina cement may be utilized without the need for a solvent to open the interconnected pores. This simplifies the creation of the[0037]protective layer42.
• Referring now to FIG. 9, the sacrificial layer[0038]24 (as shown in FIG. 5) may be etched through the gaspermeable shell42. In continuance of the above examples where thesacrificial layer24 is polysilicon, a xenon difluoride (XeF2)dry etchant52 can be used. The XeF2dry etchant52 has extremely high selectivity. It readily reacts with crystalline silicon and polysilicon, but does not react with themetal 2layer28, theprotective coating42, or various other materials. It is understood that other etchants may be used.
• As a result, the[0039]sacrificial layer24 is removed and agap54 is formed in its place. Thegap54 separates thesphere14,SiO2 layer16, andmetal 1 layer20 (collectively the “core”) from themetal 2 layer28 (the “shell”). In the present embodiment, thegap54 extends around the entire core to complete the construction of a three-axis accelerometer56.
• Referring now to FIG. 10, in yet another embodiment, a[0040]method72 for applying thecoating42 is illustrated in greater detail in steps74-80. Atstep74, a device over which the coating is to be applied and, if desirable, a substrate attached to the device are provided as described in greater detail with respect to FIGS. 11 and 12.
• Referring also to FIGS. 11 and 12, the[0041]accelerometer56 described above is illustrated without theprotective coating42 that may be applied instep34 of FIG. 1 (FIG. 11) and with the coating (FIG. 12). It should be noted that theexemplary accelerometer56 of FIGS. 11 and 12 is illustrated without anouter surface16 and withadditional electrodes28fand28g. It is understood that theaccelerometer56 is merely one example of a device that may utilize such acoating42, and many other devices of varying sizes and shapes may benefit from the application of thecoating42. In the present example, thecoating42 forms a porous, gas permeable ceramic enclosure or shell around theaccelerometer56 and its associated layers.
• Due in part to the relatively small scale of the accelerometer[0042]56 (e.g., approximately one millimeter), imperfections in the coating may create problems that might be insignificant in larger scale applications but may render theaccelerometer56 unusable. Accordingly, it may be desirable to achieve a relatively homogenous, void free layer over theaccelerometer56 with theceramic coating42.
• In the present example, the[0043]substrate40 may be made of a material such as borosilicate glass (e.g., PYREX material by CORNING GLASS WORKS CORPORATION, NEW YORK). Anaperture82 may be formed in thesubstrate40 proximate to thebumps36a,36b. Theaperture82 may be formed either before or after theaccelerometer56 is connected to thesubstrate40, depending on the particular manufacturing process used.
• In[0044]step76 of the method of FIG. 10, a vacuum (indicated byarrows84 in FIG. 12) may be applied to theaperture82 on the side of thesubstrate40 opposite theaccelerometer56 to create a suction. Vibrations may be induced instep78, as will be described later in greater detail. Accordingly, when a material such as a ceramic slurry is poured over theaccelerometer56 instep80, the suction draws a portion of the ceramic slurry over theaccelerometer56 and towards theaperture82. This may aid in the creation of a homogenous, void-free coating42 over theaccelerometer56. The amount of suction, which in turn may affect the flow of thecoating42, may depend on a number of factors, such as the rate at which the ceramic slurry is applied to theaccelerometer56, the dimensions of theaperture82, and similar factors.
• In still another embodiment, a vibrating device[0045]85 may be attached to thesubstrate40 to aid in the even distribution of the ceramic slurry over theaccelerometer56. For example, the vibrating device85 may be a piezoelectric transducer operable to create a 150 Hertz vibration. The vibrations created by the transducer may aid in homogenizing thecoating42 during application. In addition, this may aid in the prevention of voids in thecoating42. The amount of vibration, which in turn may affect the flow of thecoating42, may depend on a number of factors, such as the consistency of the ceramic slurry.
• Referring now to FIG. 13, in yet another embodiment, the[0046]protective coating42 may comprise multiple layers of porous material. This may be desirable, for example, if themetal 2layer28 and theprotective coating42 do not adhere well to one another. In the present example, theprotective layer42 includes an innerprotective layer86 that provides a desired level of adhesion with themetal 2layer28. An outerprotective layer88 can then be added that adheres well to the innerprotective layer86, but that would not adhere well to themetal 2layer28. The level of adhesion may vary with the porosity of the inner and outerprotective layers86 and88, and so the innerprotective layer86 may be less porous than the outerprotective layer88. In this manner, both adhesion and gas permeability may be achieved by using multiple layers of protective coatings.
• Referring now to FIG. 14, in still another embodiment, a[0047]sealing layer90 may be deposited on the single or multiple-layerprotective coating42 to provide a hermetic seal. As described previously, theprotective coating42 may comprise one or more gas-permeable layers that enable thesacrificial layer24 to be etched after theprotective coating42 is applied. However, in certain MEMS applications, it may be undesirable to have a porousprotective coating42. Accordingly, thesealing layer90 may be deposited onto theprotective layer42 after the etching process to seal the pores provided in theprotective layer42 for the etching process.
• In another embodiment, referring still to FIG. 14, a material (a “getter”)[0048]92 may be added proximate to thedevice56. For example, thegetter92 may be formed on thesubstrate40 and within theprotective layer42 and/or thesealing layer90. Thegetter92 may attract gas molecules during the etching process as well as gas molecules remaining after the etching process. If thesealing layer90 is deposited on theprotective layer42 after the etching process, thegetter92 may attract gas molecules that are trapped inside thedevice56 by thesealing layer90. Accordingly, thegetter92 may stabilize thedevice56.
• While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. For example, it is within the scope of the present invention to use a MEMS device of non-spherical shape. Also, it may be desirable to use materials other than ceramic for the coating. Furthermore, the coating may enter certain openings in the MEMS device. Also, it may be desirable to have multiple coatings. Therefore, the claims should be interpreted in a broad manner, consistent with the present invention.[0049]

Claims (21)

What is claimed is:

1. A method for coating a micro-electromechanical system device, the method comprising:

mounting the device on a substrate, the substrate including an aperture having a first opening proximate to the device and a second opening connected to the first opening;

applying a vacuum to the second opening; and

applying a coating material over the device;

wherein the vacuum aids in the homogeneous distribution of the coating material on the device by drawing a portion of the coating material over the device and towards the first opening.

2. The method ofclaim 1 further including applying a vibration to the device, the vibration aiding in the homogeneous distribution of the coating material over the device.

3. The method ofclaim 2 wherein the vibration is applied using a piezoelectric transducer.

4. The method ofclaim 2 further including defining an amount of vibration to be applied depending on a consistency of the coating material.

5. The method ofclaim 1 further including defining a strength of the vacuum to be applied depending on the consistency of the coating material.

6. The method ofclaim 5 further including defining the strength of the vacuum to be applied depending on the dimensions of the aperture.

7. The method ofclaim 1 further including allowing the coating material to harden into a porous enclosure.

8. A method for applying a coating layer to a micro-electromechanical system device, the method comprising:

applying a vacuum proximate to the device;

applying a vibration to the device; and

pouring a coating material over the device,

whereby the vacuum and the vibration provide a homogenous distribution of the coating material over the device.

9. The method ofclaim 8 further including allowing the coating material to harden into a gas permeable shell.

10. The method ofclaim 8 wherein the device is a sphere.

11. The method ofclaim 8 wherein the device is an accelerometer.

12. The method ofclaim 8 further including attaching the device to a substrate, the substrate including an aperture having a first opening located proximate to the device and a second opening connected to the first opening, and wherein the vacuum is applied to the second opening and exerts an attractive force that is operable to draw at least a portion of the coating material towards the first opening.

13. A method for increasing adhesion between a micro-electromechanical system device and a gas-permeable outer layer, the method comprising:

applying a gas-permeable inner layer to the device, the inner layer having a high level of adherence to the device; and

applying the outer layer over the inner layer, the outer layer having a lower level of adhesion to the device than the inner layer.

14. The method ofclaim 13 wherein the outer layer is more porous than the inner layer.

15. The method ofclaim 13 further including adding at least one gas-permeable middle layer between the inner and outer layers, the middle layer adhering to both the inner and outer layers.

16. The method ofclaim 15 wherein the middle layer is more porous than the inner layer and less porous than the outer layer.

17. A method for hermetically sealing a micro-electromechanical system device having a gas-permeable exterior coating, the method including:

providing an attractive material operable to attract gas molecules, the attractive material positioned proximate to the device; and

depositing a sealing layer over the device and the attractive material, the sealing layer operable to seal a plurality of pores present in the gas-permeable exterior coating, and the attractive material operable to attract gas molecules trapped inside the device after the sealing layer is deposited.

18. A micro-electromechanical system device, the device comprising:

an inner core;

a sacrificial layer surrounding the core;

a shell surrounding the sacrificial layer and including a first gas-permeable protective layer surrounding the shell;

so that the sacrificial layer can be etched through the first protective layer to allow the core to move within the shell.

19. The device ofclaim 18 wherein the shell further includes a second gas-permeable protective layer surrounding the first protective layer, wherein the first protective layer provides an adhesive bond between the shell and the second protective layer.

20. The device ofclaim 18 wherein the shell further includes a sealing layer, the sealing layer operable to seal a plurality of pores present in the first protective layer.

21. The device of claim20 further including an attractive material, the material operable to attract gas molecules trapped inside the sealing layer.

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